1. Field of the Invention
The present invention relates generally to electrical switching apparatus and, more particularly, to an opening assist mechanism for the cradle assembly of a circuit breaker. The invention also relates to circuit breakers having cradle assemblies with opening assist mechanisms.
2. Background Information
Switches used in electrical power distribution systems are generally old and well known in the art. Such switches include molded case circuit breakers for protecting electrical circuitry from damage due to a trip condition (e.g., without limitation, an overcurrent condition; an overload condition; an undervoltage condition; a relatively high level short circuit or fault condition; a ground fault or arc fault condition).
Molded case circuit breakers generally include an operating mechanism having at least one pair of separable contacts which are operated either manually, by way of handle disposed on the exterior of the circuit breaker housing, or automatically by way of a trip mechanism in response to the trip condition. Some trip mechanisms typically comprise an energy storage mechanism such as, for example, a spring, and a trip bar which is adapted to actuate a cradle assembly. The cradle assembly is structured to open the separable contacts in response to the trip condition. The spring or other suitable energy storage mechanism is charged by closing the switch. This operation can be performed manually, for example, by a handle and ratchet assembly, or it may be accomplished by using, for example, a motor operator. An example of the energy storage mechanism and handle and ratchet charging mechanism therefor is shown and described, for example, in U.S. Pat. No. 6,015,959, which is incorporated herein by reference.
The separable contacts of molded case circuit breakers generally include a stationary or fixed contact and a moveable contact secured to the free end of a pivotally mounted contact arm. In response to the trip condition, the cradle assembly opens (e.g., separates) the moveable contact from the stationary contact. More specifically, the cradle assembly includes a pair of toggle links and a cradle member structured to latch and unlatch the toggle links. When unlatched, for example, in response to the trip condition, the toggle links pivot the contact arm in order to open the separable contacts. The toggle links are pivotally coupled (e.g., pinned) with respect to one another and to the cradle member, and generally comprise an over-center toggle mechanism wherein one of the toggle links is adapted to engage a latching surface on the cradle member in order to latch the cradle assembly when the circuit breaker is not tripped. Accordingly, when that toggle link is disengaged from the latching surface on the cradle member, the operating assembly causes the separable contacts to be opened. The circuit breaker trip bar also engages the toggle link and, in a normal position, the trip bar allows the toggle link to latch the cradle assembly. However, when the trip bar is rotated, the toggle link becomes disengaged from the latching surface on the cradle member to allow the operating mechanism to trip or open the separable contacts. A more detailed description of the operation of the operating assembly can be found, for example, in U.S. Pat. No. 6,541,727, which is incorporated herein by reference. Such operating assembly or a comparable version thereof is commonly employed in a wide variety of electrical switching apparatus other than, and in addition to, the molded case circuit breaker described hereinbefore.
Although the foregoing operating assembly and, in particular, the cradle assembly thereof, is a relatively tried and true design, it suffers from a number of unique disadvantages under certain circumstances. Specifically, the toggle links of the over-center toggle mechanism might lock or become jammed or wedged in the over-center configuration. The over-center configuration occurs when the separable contacts are closed (e.g. when the circuit breaker is ON). Jamming of the toggle links in the over-center configuration can result in the cradle assembly, and thus the operating mechanism, becoming “stuck” in the ON position. This may disadvantageously prohibit the circuit breaker from tripping and could, therefore, result in severe damage occurring to electrical equipment in communication with the breaker. It could also result in the general inability to turn the circuit breaker OFF. In order to alleviate these potentially dangerous circumstances, there is a need for a mechanism which is adapted to dislodge or initiate movement of the toggle links of the cradle assembly from the over-center position.
There is, therefore, room for improvement in opening assist mechanisms for cradle assemblies and in circuit breakers employing the same.